There is something called VPN
It is very easy to take an U.S. ip if you know how to do it. You may even do it for free. And since B&N doesn't want any credit card info with every purchase, using free VPNs are safe too.
B&N says that I can only buy digital content if I have an U.S. or Canada billing address. I bought an address in U.S. from MyUSABox and told my bank to add it to my MasterCard account. You can also register Nook outside North America.